Stereotactical instrument

ABSTRACT

A stereotactical instrument for identifying a spatial position of an area in a patient&#39;s body which is to be subjected to treatment, preferably radiation treatment, the position of the area being previously determined, for example, by an angiogram, PET, DSA, CT, MRI, or X-ray equipment. The instrument includes a non-yielding and radiolucent frame which is arranged to support the patient&#39;s body and to support an indicating device, a radiolucent fixing device which is arranged inside the frame and on which the patient&#39;s body is intended to rest, the fixing device including a flexible casing which contains a yieldable substance, at a first stage the fixing device being adapted to permit that the patient is oriented in a desired position, partly sunk into the fixing device, and at a second stage the yieldable substance of the fixing device being given a non-yielding state, thereby fixing the patient in the desired position, and a partially non-radiolucent orienting device which is mounted on at least one longitudinal side of the frame and which is adapted to indicate the position of an image sectional plane through the area in the patient&#39;s body.

The present invention relates to a stereotactical instrument foridentifying, by means of image sectional planes or markers, the spatialposition of an area in a patient's body which is to be subjected totreatment, preferably radiation treatment, the position of the areabeing previously determined, for example by means of angiogram, PET,DSA, CT, MRI or X-ray equipment. The instrument comprises a non-yieldingand radiolucent frame which is arranged to support the patient's bodyand to support an indicating device, a radiolucent fixing means which isarranged inside the frame and on which the patient's body is intended torest. The fixing means comprises a flexible casing which contains ayieldable substance, at a first stage the fixing means being adapted topermit that the patient be oriented in a desired position, partly sunkinto the fixing means, and at a second stage the yieldable substance ofthe fixing means being given a non-yielding state, thereby fixing thepatient in the desired position.

In radiation treatment as well as in surgical operations, the ability toidentify the target area with great accuracy is highly important. Tominimise the risk, the surgeon must be sure of hitting the correct areain the treatment.

It is vital that the treatment area can be easily and safely identifiedon different occasions, since, for example, fractionated radiationtreatment requires a number of successive treatment sessions.

U.S. Pat. No. 5,147,372 discloses a computerised tomography unit whichcomprises a radiation-damping and perforated biopsy arch which isdisplaceably and pivotally attached to the treatment table on which thepatient is placed. By means of the X-ray radiation in CT equipment, asectional image is obtained in which the biopsy arch is outlined, asuitable hole in the biopsy arch being selectable for introducing aneedle point in the target area. Although this prior art unit permits ina simple way the target area to be found, the accuracy is jeopardised bythe patient not being fixed to the treatment table. Besides, the unit isnot intended for radiation treatment.

The object of the present invention is to provide a stereotacticalinstrument with high accuracy when identifying the target area.

A further object of the invention is to provide a stereotacticalinstrument which permits safe and repeatable identification of thetreatment area.

According to the invention, these objects are achieved by means of aninstrument as described above, which is characterised by a partiallynon-radiolucent orienting means which is mounted on at least onelongitudinal side of the frame and which is adapted to indicate theposition of the respective image sectional plane through said area inthe patient's body, and by the orienting means comprising a first arrayof lines of different lengths.

Further developments of the invention are describe below.

A preferred embodiment of the invention will now be described for thepurpose of exemplification, reference being made to the accompanyingdrawings in which:

FIG. 1 is a perspective schematic view of a patient testing in the frameof an embodiment of the instrument; and

FIG. 2 illustrates an image sectional plane and its orientation thestereotactical system of coordinates.

The inventive stereotactical instrument, which generally designated 1 inFIG. 1, comprises an elongate, non-yielding frame 2 which is made of amaterial that does not cause any artifacts (disturbances) in the images,i.e., a material which is translucent to X-rays and other radioactiveradiation. A fixing means 3 is adapted to be inserted in the frame 2which is open at the top and at the ends, said fixing means comprising aflexible casing which is impermeable to fluid and hermetically enclosesa yielding substance, not shown in FIG. 2. On this fixing means, thepatient is caused to take the desired position for diagnostics ortreatment, the patient partially sinking into the yieldable fixingmeans, and a large contact surface against the patient is obtained, seeFIG. 2. Subsequently, the fixing means 3 is given a non-yielding stateso as to fix the patient in the desired position. This can be achievedby the casing of the fixing means holding a plurality of small bodies,for example so-called Frigolit beads or the like, which are fixed intheir respective positions when a negative pressure is produced in theimpermeable casing. It is also possible to fill the casing with a fluidwhich can be caused to solidify so as to keep its enforced shape. Thus,the casing can be filled with prepolymerised polyurethane foam which,when the patient has been oriented in the desired position, is caused tofinally polymerise and thus form a non-yielding, fixing compound. Bymeans of a first indicating device 4 fixedly arranged on the frame 2 inthe longitudinal direction thereof, and a second indicating device 5arranged on an arch 6 which is displaceable on the frame in thelongitudinal direction thereof, the patient can be oriented in thefixing means for treatment of an area which has previously been locatedby means of computerised tomography, X-rays etc.

The frame 2 is preferably formed with fixing holes (not shown) intowhich the fixing means can penetrate a; its first, yielding stage,and/or fixing lugs 7 penetrating into the fixing means so as to fix thisat its second, non-yielding stage.

Finally, the frame 2 comprises one or more orienting means 8 along eachlongitudinal side of the frame. The orienting means 8 which preferablyis releasably attached to the inside of the frame, consists of aradiolucent support with three arrays of lines preventing radiation,which are made of, e.g., wire, strips or thin sections of copper fordiagnostic X-ray, angiography, DSA and CT examinations or gas-, liquid-or substance-filled tubes for diagnostic PET and MRI examinations. Thefirst array 10 comprises a number of lines of different lengthsextending in parallel from one open end of the frame, said linespreferably being parallel also with the bottom of the frame, as shown inFIG. 1. The second array 11 comprises parallel lines extending at anangle to the first array 10 and extending from the first array alongeach longitudinal side of the frame. The second array 11 is terminatedat a third array 12 adjacent the upper edge of the longitudinal side.The third array 12 comprises one or more unbroken lines which preferablyare parallel with the lines of the first array. See also FIG. 2 whichschematically illustrates a vertical section of the orienting means 8.In this Figure, the frame 2 is indicated by full lines and the uppersurface of the fixing means 3 by dashed lines.

The frame 2 is supported by a bed unit which allows the patient to bemoved, fixed in the frame.

The diagnostic equipment produces an image section, for example an MRIor CT sectional image, and the orientation of this section is indicatedby the orienting means 8. By counting the number of lines in the firstarray 10, a base value is obtained. The distance between the uppermostunbroken line in the first array and the point in which the imagesection cuts one of the inclined lines in the second array is measuredand yields a supplementary value, see FIG. 2. Since the distance betweenthe two upper horizontal marks 11 and 12 is known, this distance can beused as a reference for calculating the vertical coordinate in the imagesectional plane. Similarly, the horizontal coordinate in the image planecan be calculated by the distance between 11 and 12 on the two sides ofthe frame being known. By means of these values, the orientation of theimage section can be determined with great accuracy. It should be notedthat the image section need not be oriented at right angles to thelongitudinal axis of the frame 2, but may be oriented at an optionalangle, as shown in FIG. 2 in which each point of intersection betweenThe image section and the associated line in The second array 11 ispositioned on different levels. This Figure schematically illustrates asectional image of the patient in which the target area or treatmentarea 13 appears. In diagnostic use, the orienting accuracy of thestereotactical system has been about 1 mm, and in repeated treatmentusing the stereotactical instrument the orienting accuracy has beenabout 3 mm in the transverse plane and about 6 mm in the longitudinalplane. These values were obtained for target areas close to thediaphragm and were to a certain extent affected by the patient'sbreathing. In order to reduce the effect of the breathing movements, anabdomen belt (not shown) may be used on such occasions.

The stereotactical coordinates are adjusted on the scales 4 and 5 in thetreatment room by means of prior-art wall-mounted lasers, mounted-andset in conventional manner, which define the system of coordinates forthe room/treatment unit. Guided by the values which are obtained in thelocating of the target point, i.e. the tissue area To be treated, andwhich are transferred to the stereotactical instrument, the coordinatesare obtained which are necessary to be able to set a radiation source,starting from the frame, such that the beam therefrom is directed to thetreatment site or target point.

The invention is not restricted to that described above and illustratedin the drawings, but may be modified within the scope of the claims.

I claim:
 1. A stereotactical instrument for identifying a spatialposition of an area in a patient's body which is to be subjected totreatment, the spatial position of the area having been previouslydetermined, the instrument comprising:a non-yielding and radiolucentframe which is arranged to support the patient's body; a radiolucentfixing means which is arranged inside the frame and on which thepatient's body is intended to rest, said fixing means comprising aflexible casing which contains a yieldable substance, the fixing meansbeing adapted to permit the patient to be partly sunk into the fixingmeans and oriented in a desired position at a first stage, and theyieldable substance of the fixing means being transformable into anon-yielding state to fix the patient in the desired position at asecond stage; and a partially non-radiolucent orienting means which ismounted on at least one longitudinal side of the frame and which isadapted to indicate the position of an image sectional plane throughsaid area in the patient's body, the orienting means comprising a firstarray of parallel lines of different lengths and a second array ofparallel lines extending at an acute angle to the first array ofparallel lines, all of said lines blocking radiation.
 2. Astereotactical instrument as claimed in claim 1, wherein the framecomprises at least one of fixing holes and fixing lugs for preventingrelative movement between the frame and the fixing means when in thesecond stage.
 3. A stereotactical instrument as claimed in claim 1,wherein the orienting means comprises a third array of at least oneunbroken line disposed at an opposite side of the second array from thefirst array, said third array being parallel with the first array.
 4. Astereotactical instrument as claimed in claim 1, wherein said lines ofsaid first and second arrays are made of copper wire arranged on aradiolucent support.
 5. A stereotactical instrument as claimed in claim1, wherein said lines of said first and second arrays are made of tubeswhich are filled with a substance, for at least one of PET and MRIdiagnostics.
 6. A stereotactical instrument as claimed in claim 4wherein the orienting means is releasably attached to the frame.
 7. Astereotactical instrument as claimed in claim 3, wherein said lines ofsaid first, second, and third arrays are made of copper wire arranged ona radiolucent support.
 8. A stereotactical instrument as claimed inclaim 3, wherein said lines of said first, second, and third arrays aremade of tubes which are filled with a substance, for at least one of PETand MRI diagnostics.
 9. A stereotactical instrument claimed in claim 3,wherein the orienting means is releaseably attached to the frame.
 10. Astereotactical instrument as claimed in claim 1, wherein the treatmentis radiation treatment.
 11. A stereotactical instrument as claimed inclaim 1, wherein the position of the area has been previously determinedby one of angiogram, PET, DSA, CT, MRI, and X-ray equipment.
 12. Astereotactical instrument as claimed in claim 1, wherein the frame isarranged to support an indicating device.